Surgical Testing Instrument and System

ABSTRACT

The present disclosure describes an instrument for measuring the dielectric properties of biological tissue. The instrument includes a top electrode assembly and a bottom electrode assembly, the top electrode assembly including a top electrode and at least one shaft adjustably positionable to move the top electrode relative to the bottom electrode assembly, the bottom electrode assembly including a bottom test plate and a bottom electrode. The instrument also includes a testing cylinder coupled to the shaft and having an inner cavity defined therein that houses the top electrode and which is designed to enclose the bottom electrode therein. The testing cylinder is configured to reduce at least one of electric current, magnetic current, stray radiative RF fields and external capacitive leakage currents during activation of the top and bottom electrodes.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/487,295 by Podhajsky et al., filed Jul. 14, 2006, now U.S. Pat. No.7,443,175.

TECHNICAL FIELD

The present disclosure relates to a surgical testing instrument. Moreparticularly, the present disclosure relates to an apparatus and systemfor measuring dielectric properties of biological tissue.

BACKGROUND

Radio frequency or RF energy is commonly used in a variety of differentsurgical operations. However, body tissues that are subjected to veryhigh levels of RF energy may suffer some residual heat damage.Therefore, prior to the use of RF energy on a particular patient it isoften desirable to develop computer simulated heat transfer and electricfield models of the heat transfer to tissue using computer programs.

When an electric charge is applied across a material, in this casetissue, a charge and current are created in the material. The density ofcharge is referred to as the permittivity (ε) while the density ofcurrent is called the conductivity (σ). These two properties are largelyresponsible for the response of different tissue types to an arbitraryRF electric field and should be included in any accurate computermodeling. Moreover, by comparing the electrical properties of healthyand abnormal tissue it may be possible to detect the onset of certainkinds of pathologies or sicknesses.

Testing methodologies exist for determining the permittivity andconductivity of a given material. However, a number of thesemethodologies contain numerous sources of error that affect the accuracyof the measurement, which may be detrimental to accurate tissue heattransfer modeling.

SUMMARY

The present disclosure relates to an instrument for measuring thedielectric properties of biological tissue and other materials. Theinstrument includes a top electrode assembly and a bottom electrodeassembly, the top electrode assembly including a top electrode and atleast one shaft adjustably positionable to move the top electroderelative to the bottom electrode assembly, the bottom electrode assemblyincluding a testing plate and a bottom electrode. The instrument alsoincludes a testing cylinder coupled to the shaft and having an innercavity defined therein that houses the top electrode and which isdesigned to enclose the bottom electrode therein. The testing cylinderis configured to reduce at least one of electric current, magneticcurrent, stray radiative RF fields and external capacitive leakagecurrents during activation of the top and bottom electrodes.

According to one embodiment of the present disclosure a system formeasuring the dielectric properties of biological tissue is provided.The system includes an analyzer configured to measure the properties ofthe tissue. The system also includes a top electrode assembly and abottom electrode assembly, the top electrode assembly having a topelectrode and at least one shaft adjustably positionable to move the topelectrode relative to the bottom electrode assembly, the bottomelectrode assembly having a testing plate and a bottom electrode. Inaccordance with this embodiment a testing cylinder is coupled to theshaft and includes an inner cavity defined therein that houses the topelectrode and which is designed to enclose the bottom electrode therein,the testing cylinder is configured to reduce at least one of electriccurrent, magnetic current, stray radiative RF fields and externalcapacitive leakage currents during activation of the top and bottomelectrodes. The system further includes a graphical user interfaceconfigured to control the analyzer.

The present disclosure also relates to a method for measuring thedielectric properties of biological tissue is provided. The methodincludes the step of providing a top electrode assembly and a bottomelectrode assembly, the top electrode assembly including a top electrodeand at least one shaft adjustably positionable to move the top electroderelative to the bottom electrode assembly, the bottom electrode assemblyincluding a bottom test plate and a bottom electrode. The method alsoincludes the step of coupling a testing cylinder to the shaft, thetesting cylinder having an inner cavity defined therein that houses thetop electrode and which is designed to enclose the bottom electrodetherein, the testing cylinder being configured to reduce at least one ofelectric current, magnetic current, stray radiative RF fields andexternal capacitive leakage currents during activation of the top andbottom electrodes. The method further includes the step of connecting ananalyzer to the top electrode assembly and the bottom electrodeassembly, the analyzer being configured to measure and analyze thedielectric properties of biological tissue.

According to a further aspect of the present disclosure a method formeasuring the dielectric properties of biological tissue is disclosed.The method includes the steps of providing a top electrode assembly, abottom electrode assembly and a testing plate. The top electrodeassembly includes a top electrode and at least one shaft adjustablypositionable to move the top electrode relative to the bottom electrodeassembly. The bottom electrode assembly includes a bottom electrode. Thetesting plate is disposed between the top electrode assembly and abottom electrode assembly and includes a selectively conformable insertcavity therein. The method also includes the step of inserting a tissuesample into the selectively conformable insert cavity and forming thetissue sample by cutting any excess tissue to fit the tissue sample intothe insert cavity. The method further includes the step of coupling atesting cylinder to the shaft. The testing cylinder includes an innercavity defined therein that houses the top electrode and is designed toenclose the bottom electrode therein. The testing cylinder is configuredto reduce at least one of electric current, magnetic current, strayradiative RF fields and external capacitive leakage currents duringactivation of the top and bottom electrodes.

According to another aspect of the present disclosure a system formeasuring dielectric properties of biological tissue is disclosed. Thesystem includes a top electrode assembly and a bottom electrodeassembly. The top electrode assembly includes a top electrode and atleast one shaft adjustably positionable to move the top electroderelative to the bottom electrode assembly. The bottom electrode assemblyincludes a testing plate configured to receive the tissue and a bottomelectrode. The system also includes a testing cylinder coupled to theshaft. The testing cylinder includes an inner cavity defined thereinthat houses the top electrode and is designed to enclose the bottomelectrode therein. The testing cylinder is configured to reduce at leastone of electric current, magnetic current, stray radiative RF fields andexternal capacitive leakage currents during activation of the top andbottom electrodes. The system further includes a high frequencyelectrosurgical generator configured to supply high frequency electricalenergy to the tissue through at least one of the top electrode and thebottom electrode and an analyzer configured to measure the properties ofbiological tissue in response to high frequency electrical energy.

According to yet another aspect of the present disclosure, a system formeasuring the dielectric properties of material is disclosed. The systemincludes a top electrode assembly and a bottom electrode assembly. Thetop electrode assembly includes a top electrode and at least one shaftadjustably positionable to move the top electrode relative to the bottomelectrode assembly. The bottom electrode assembly includes a testingplate configured to receive the material and a bottom electrode. Thesystem also includes a testing cylinder coupled to the shaft and havingan inner cavity defined therein that houses the top electrode and whichis designed to enclose the bottom electrode therein. The testingcylinder is configured to reduce at least one of electric current,magnetic current, stray radiative RF fields and external capacitiveleakage currents during activation of the top and bottom electrodes. Thesystem also includes an analyzer configured to measure the properties ofthe material. The analyzer includes a generator configured to supplyelectrical energy to the material through at least one of the topelectrode and the bottom electrode, wherein the analyzer is connected tothe top electrode assembly, the bottom electrode assembly and thetesting cylinder through a plurality of cables each having a wire, ashield and an insulator therebetween, the wires being connected to thetop electrode and the bottom electrode and the shield being connected tothe testing cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the subject instrument are described herein withreference to the drawings wherein:

FIG. 1 is a perspective view of one embodiment according to the presentdisclosure shown in an open position;

FIG. 2 is a side perspective view of the instrument shown in FIG. 1;

FIG. 3 is an exploded view of the instrument shown in FIGS. 1-2;

FIG. 4 is a perspective view of the instrument shown in FIGS. 1-3 shownin the closed position;

FIG. 5 is a cross-sectional view of the instrument shown in FIGS. 1-4shown in the open position;

FIG. 6 is a cross-sectional view of another embodiment of the systemaccording to the present disclosure;

FIG. 7 is a cross-sectional view of the system of FIG. 6 shown beingactuated;

FIG. 8 is a schematic illustration of the present disclosure; and

FIGS. 9 a-c are electrical schematic illustrations of the presentdisclosure showing four terminal pair connections.

DETAILED DESCRIPTION

Referring initially to FIGS. 1, 2, 3 and 5, one embodiment of a surgicaltesting instrument 100 is shown in an open position. Testing instrument100 includes an L-shaped support base 106 having a back plate 106 a andan elongated flange 106 b extending from a bottom end thereof. A bracketsupport 106 c is positioned between the back plate 106 a and theelongated flange 106 b to provide additional support to the support base106. An elongated rib 107 extends from the back plate 106 a parallel toflange 106 b. Rib 107 includes a top portion 107 a that is configured tosupport a top electrode assembly 140 and a bottom portion 107 b thatabuts against a bottom electrode assembly 150.

Support unit 106 and rib 107 may be constructed of a rigid materialcapable of providing structural support. Support base 106 and rib 107may be constructed from a variety of different materials, including, butnot limited to, metallic, ceramic, polymeric and wooden materials.

Top electrode assembly 140 includes a coupler 141 that securely engagesthe top portion 107 a of rib 107 and is configured to include a lumen141 a defined therein (see FIG. 5) for slidingly receiving an elongatedshaft 144. Elongated shaft 144 includes a slide rod 144 a that securelymates with an electrode mandrel 144 b, which in turn, secures anelectrode 142 for testing dielectric properties of matter (e.g., livingtissue). Mandrel 144 b may include a top portion 144 b′ with a differentor ergonomically-friendly geometry to facilitate handling thereof, e.g.,for mounting the electrode 142 to the mandrel 144 b.

Top electrode assembly 140 also includes first and second cylinders 145a and 145 b that concentrically mate to receive and secure the electrode142 and mandrel therein for testing purposes. More particularly,cylinder 145 b includes a two-staged inner lumen 145 b″ defined therein(See FIG. 5) that is dimensioned to receive a mounting collar 147 in thelower portion thereof and elongated shaft 144 in the upper portionthereof. Mounting collar 147, in turn, includes a centrally disposedlumen 147′ dimensioned to receive and secure the electrode 142 and thebottom portion of the mandrel 144 b.

The first cylinder 145 b is formed from a suitable conductive materialsuch as copper, stainless steel, chromium, nickel, or an alloy which isany combination of these and similar metals and the like. The secondcylinder 145 b is formed from a suitable dielectric material havingdesirable insulative properties, such as Teflon and the like. Thecylinder 145 b is dimensioned such that it occupies substantially theentirety of the lumen of the first cylinder 145 a to ensure that thespace between the testing sample, the electrodes, and the first cylinder145 b is not occupied by air or other foreign substances. It has beendetermined that arranging the cylinders 145 a and 145 b in this fashionremoves errors generated during testing which are caused by theelectrical test signals passing through surrounding atmosphere (e.g.,arcing conditions through air). In lieu of the second cylinder 145 bvarious other dielectric solid and non-solid materials may be used(e.g., liquid). Those skilled in the art will appreciate themodifications which have to be made to the disclosed electrode andcylinder configurations to accommodate liquid insulators.

Cylinder 145 b also includes an aperture 149 b defined therein that isdimensioned to receive a pin 146 that is movable from a first positionto secure the electrode 142 and mandrel 144 b within cylinder 145 b to asecond position that releases the mandrel 144 b and electrode 142 fromwithin the cylinder 145 b. Cylinder 145 a is designed to concentricallymate with cylinder 145 b and includes an aperture 149 a defined thereinthat aligns with aperture 149 b to facilitate access to pin 146.Mounting collar 147 also includes an aperture 147 a defined therethroughthat receives locking element 146 a of pin 146 that optionally locks theelectrode 142 in place for testing. The mounting collar 147 is formedfrom a conducting material, such as copper, stainless steel, chromium,nickel, or an alloy which is any combination of these and similar metalsand the like. The mounting collar 147 is in physical and electricalcontact with the electrode 142. During operation, electrical signals arepassed to the electrode 142 through the pin 146 and the locking collar147. The electrode 142 may be disposed slidingly within the mountingcollar 147 allowing for selective adjustment of the vertical positionand pressure of the electrode 142 on the testing sample. A plate 148encloses the top of cylinder 145 a. The plate 148 includes a throughhole 148 a defined therein that permits the elongated shaft 144 to slidetherethrough during testing and/or mounting of the electrode 142.

Bottom electrode assembly 150 includes mounting plate 152 having aseries of apertures 152 a defined therein (See FIG. 3) that align withcorresponding apertures 106 d to secure the bottom electrode 150 toflange 106 b. For example, apertures 152 a are configured to receivelocking mechanisms (not shown) such as pins, bolts, screws or the liketo secure the bottom electrode assembly 150.

Circular coupling unit 154 is operatively connected to mounting plate152 and defines an aperture 154 a that is configured to receive a pin156. Coupling unit 154 is configured to receive a circular washer 158that is operatively connected to coupling unit 154 by way of athread-fit, snap-fit or other mating arrangement. Circular washer 158may define a groove 158 a that is configured to hold ring 160. Tubularmember 162 is configured to extend longitudinally within ring 160 andincludes aperture 162 a. Tubular member 162 is generally circular innature and is configured to receive cylindrical member 164. Cylindricalmember 164 includes a hole 164 a that aligns with hole 154 a to receivepin 156. Cylindrical member 164 also includes a passageway 164 b definedin a top portion thereof that is dimensioned to receive electrode 166therein. Electrode 166 is operatively connected with inner testing ring168 and is configured to hold tissue therein.

Pin 156 extends through coupling unit 154, tubular member 162 andcylindrical member 164, and more particularly, through aperture 154 a,aperture 162 a and hole 164 a. Pin 156 includes locking element 156 athat is configured to secure cylindrical member 164 within bottomelectrode assembly 150, more particularly, locking element 156 a ismovable from a first position to secure bottom electrode 166 withincylindrical member 164 to a second position that releases bottomelectrode 166 from cylindrical member 164. During operation, electricalsignal are passed to or from the electrode 166 through the pin 156 andthe cylindrical member 164. Those skilled in the art will appreciatethat the electrodes 142 and 166 may be used interchangeably as active orreturn electrodes.

As mentioned above, top electrode 142 is coupled to shaft 144 and isadjustably positionable to move in a general vertical direction. Bottomelectrode 166 is housed within inner testing ring or plate 168 and isconnected to cylindrical member 164. Inner testing plate 168 includes alumen 169 which serves as an insert cavity to house the testing samplebeing measured. The testing plate 168 may be constructed out of avariety of different materials including, but not limited to, suitableinsulated material, such as Teflon and the like. Testing plate 168 mayalso be configured to prevent tissue from expanding or deforming in anydirection, therefore providing a more even tissue distribution. Testingplate 168 may be circular, square, oval or any other suitable shape andmay be selectively formable for a particular tissue type. Moreover,testing plate 168 may rest upon bottom electrode 166 or include one ormore mechanical interfaces that facilitate alignment with bottomelectrode 166.

Electrodes 142, 166 are configured to move in substantial verticalregistration relative to one another for testing purposes. Top andbottom electrodes 142, 166 may be detachably mounted to apparatus 100 toaccommodate for sterilization and tissue preparation. Top and bottomelectrodes 142, 166 may be constructed out of a number of differentmaterials including, but not limited to, stainless steel, copper, brass,cobalt-based alloy, titanium, copper, chromium, nickel, or an alloywhich is any combination of these and similar metals and the like. Thesematerials can be readily sterilized and are used in medical devices dueto their anti-corrosive properties.

As mentioned above, cylinders 145 a and 145 b surround electrode 142.The second cylinder 145 b is constructed of an insulative material thatis designed to eliminate or reduce stray capacitance, which is a majorcause of measurement error in surgical testing equipment, particularlythose that deal with dielectric materials. As explained in more detailbelow, when the testing unit is moved from an open tissue mountingposition to the testing position, cylinders 145 a and 145 b surroundboth electrodes 142 and 166. The insulative material may be selectedfrom a variety of different materials, including, but not limited to,polymerics, ceramics and glass.

FIGS. 2 and 5 show the testing unit 100 in an open position for loadingtissue and FIGS. 4 and 6 show the testing unit 100 in a closed positionfor testing tissue. More particularly, once the two electrodes 142 and166 are assembled in their respective top and bottom electrodeassemblies 140 and 150 as shown in FIG. 3, the testing unit 100 isreadied to receive and test tissue. In the open position, cylinders 145a and 158 reside in generally vertical registration relative to oneanother for loading biological tissue atop testing plate 168.

Tissue is placed within the lumen 169 and is shaped to ensure that thetissue occupies the entire volume of the thereof so that the tissuesample is in substantially complete contact with the electrodes 142 and166. This may be accomplished by initially placing an excessive amountof the tissue sample into the lumen 169 and then cutting the excesstissue to fit the lumen. Cutting may be accomplished by sliding acutting instrument (e.g., scalpel) along the periphery of the topsurface of the testing plate 168 thereby using the surface as a guide toensure that the tissue sample occupies the lumen 169. To further ensurethat tissue contact between the electrodes 142 and 166 is thorough(e.g., no empty space exists between the sample and the electrodes)hydrogel inserts may be placed therebetween.

Electrodes 142 and 166 could be constructed into a variety of differentshapes including, but not limited to, circular, square, polygonal andoval. Moreover, electrodes 142 and 166 could have varying degrees ofthickness. Electrodes 142 and 166 also include a connection through thepins 146 and 156 that allows the electrodes to connect with cables,which are discussed below. The electrodes 142 and 166 and the testingplate 168 are detachable and can have various shapes such that the shapeof the lumen 169 (e.g., the insert cavity) is selectively conformable tovarious types of tissue and/or materials being tested. The modularconstruction of the instrument 100, in particular the electrodes 142 and166 and the testing plate 168 also allows for easy cleaning andsterilization of these components. Thus an insert cavity having acylindrical shape may be used for testing liver tissue, whereas arectangular shaped cavity may be used for testing dielectric materials.

Once the tissue is placed into the testing plate 168, the testing unit100 may be moved to the so-called testing position. More particularly,when the user is ready to test the tissue, the user manipulates theshaft 144 (e.g., by moving mandrel 144 b towards the bottom electrodeassembly 150), which in turn, moves the cylinder 145 a relative tocylinder 158 to enclose the tissue within the inner cavity 149 c definedin cylinder 145 a around electrode 142 (see FIGS. 4 and 6). In theclosed position, electrode 142 and 166 are positioned to engage thetissue for testing purposes. Moreover, when cylinders 145 a and 158meet, the cylinders 145 a and circular washer 158 form an enclosure orshield 190 around the electrodes 142 and 166 and the tissue. In oneparticular embodiment, the cylinder 145 a with a bottom portion (e.g.,the circular washer 158 and the ring 160) act as a Faraday cage toreduce or eliminate stray magnetic fields during activation which asmentioned above, allows the test fixture to obtain more reliable andaccurate results.

In the closed testing position, the vertical position of the electrode142 may be adjusted to apply variable mechanical pressure on the tissuesample within the testing plate 168 to ensure that the tissue contact ismaintained between tissue and the electrodes 142 and 166. This alsoremoves any empty space (e.g., air) within the lumen 169. The tissueengaging surface of the electrodes may also be polished to assurecontinuity with the tissue for testing purposes.

The coupler 141 guides the elongated shaft 144 and allows for verticalpositioning of the electrode 142. In particular, vertical position ofthe electrode 142 is directly related to the compression and/or pressureexerted on the testing sample. The coupler 141 may include a pressuretransducer (not explicitly shown) or another apparatus (e.g., graphicalscale) for measuring the pressure exerted by the electrode 142 on thetesting sample. This allows for testing effects of pressure on thedielectric properties of the testing sample. In particular, by varyingpressure during testing, the relationship between viscoelasticproperties and tissue conductivity and permeability may be tested.

FIG. 5 shows instrument 100 held in the open position having an extendedgap distance “g”. The gap distance “g” between electrodes 142 and 166may be controlled using adjustable mechanism or pin 146. Testinginstrument 100 may be adjusted, using this mechanism, between open,closed and various measurement positions respectively. Alternatively,FIG. 6 shows instrument 100 in the closed position having a reduced gapdistance “g”. Adjustable mechanism 146 may include knobs, latches,switches, levers or any other suitable device configured to alter thegap distance “g” between electrodes 142 and 166.

Referring again to FIGS. 6-7, instrument 100 may be used as part of asystem 200 that includes an impedance analyzer 280, a plurality ofconnection cables 282 and a graphical user interface 284. Dielectrictesting is used to determine the frequency response of the permittivityand conductivity of a material. This means that the material will beexposed to a specific frequency from a voltage source while the currentflowing through the material is measured. From this information, themagnitude of the impedance and the phase shift between the voltage andcurrent time signals is determined. This entire process is repeated atdifferent frequencies so that a graph of magnitude of impedance vs.frequency and a graph of phase vs. frequency for a given material can becreated. Impedance analyzer 280 is configured to perform these tests. Inaddition to displaying the impedance and phase of a material at aspecific excitation frequency, analyzer 280 also has the capability ofoutputting various equivalent forms of the impedance and phase of a testmaterial.

Analyzer 280 is configured to measure a variety of different parametersof biological tissue. Some of these may include, but are not limited to,gain, phase, capacitance, impedance, conductance, dissipation factor andloss tangent. Analyzer 280 is controlled using a graphical userinterface (GUI) 284 that is configured to control analyzer 280 through acommunications port, such as a general purpose interface bus (GPIB).Connection cables 282 are configured to connect impedance analyzer 280with top and bottom electrodes 142 and 166.

Referring now to FIG. 8 an electrical schematic of the impedanceanalyzer 280 connected to the instrument 100. Connection or BNC cables282 are commonly used to transmit electrical signals. BNC cables 282carry the signal along a wire on the axis of the cable. This wire issurrounded with an insulator, which is wrapped with a braided shield.Normally, this shield is connected to ground via the BNC connector atthe ends of the cable, although the connectors may allow the shield to“float” to varying voltages. The shield is very helpful in isolating theinner conductor from stray RF and capacitive leakage fields as well asany magnetic fields, which would produce noise.

BNC cables 282 are used to eliminate the effect of test signal losses incables 282 as well as to match the impedance of cables 282 to theimpedance of instrument 200. The signal loss of BNC cables 282 isminimized by monitoring the signal at the tissue under test andproviding corrective compensation at the signal source at the cable,which contributes frequency dependent errors to the measurement oftissue conductivity and permittivity.

As shown in FIG. 8, the outer shields of the low potential and current(Lp and Lc) terminals are connected to a BNC-T connector 283 which isthen connected to the pin 146. The high potential and high current (Hpand Hc) terminals are connected to a BNC-T connector 285 which is thenconnected to the pin 156. As discussed above, the pin 146 iselectrically connected to the electrode 142 and the pin 156 iselectrically connected to the electrode 166. The BNC-T connectors 283and 285 include wire interconnects and shield interconnects which areinsulated from one another. The BNC-T connectors 283 and 285 and thepins 146 and 156 connect the wires of the BNC cables 282 to therespective electrodes 142 and 166 while the ground shielding of the BNCcables 282 are connected to the first cylinder 145 a and the couplingunit 154. As a result, the first cylinder 145 a in conjunction with thecircular washer 158 and the ring 160 act as a cylindrical RF shieldcontainment vessel which provides continuity for the coaxial outershields and a low-impedance low-loss signal return path independent oftester operating frequency. In particular, the RF shield containmentvessel reduces stray radiative RF fields and external capacitive leakagecomponents which are known to corrupt measurement integrity andintroduce significant error.

Analyzer 280 has four output terminals across which instrument 100 isconnected. There are five different available configurations forconnecting instrument 100 to analyzer 280, all of which have varyinglevels of accuracy and setup difficulty. The most accurate of the fivemethods is called the four terminal pair (4TP) configuration.

FIGS. 9A-B show a connection diagram and a schematic of the 4TPconnection setup. Four-terminal pair wiring provides localized tissuemetering to minimize fixture error. The current flows out of the digitalsignal generator or analyzer 280 at the high current (Hc) terminal andinto instrument 100, the device under test (DUT). The Hc terminal isconnected to an AC generator 299. From there, the current flows into thelow current (Lc) terminal where an ammeter measures only the currentthat flows through the electrode connected to the Lc terminal or topelectrode 142. The low voltage side of the ammeter is connected to themeasuring circuit ground. The measuring circuit ground level is referredto as the “guard ground.” This guard ground is connected back to thedigital signal generator or analyzer 280 and is also connected to theground sheaths of the four output BNC terminals of analyzer 280. Theconnections shown in FIG. 9 are made with BNC connectors, and the outerconducting sheath of each BNC cable is connected together. This meansthat the return current flowing through cables 282 is the same as thecurrent flowing through the inner cable of the BNC connector, thuscanceling any field effect caused by the inner cable.

FIG. 9C shows the typical impedance measurement range, shown in ohms(Ω). Analyzer 280 utilizes an auto balancing bridge to detect theimpedance across instrument 100. Analyzer 280 measures the magnitude ofthe impedance as well as the phase difference between the applied ACvoltage and the measured AC current. Analyzer 280 measures the currentpresent at top electrode 142. A measurement signal is always produced atbottom electrode 166 while top electrode 142 is continually maintainedat a OV potential by analyzer 280.

The AC generator 299 (which provides electrical signals through the Hcterminal) may be an electrosurgical generator or any generator capableof producing high frequency energy since the RF shield allows for highfrequency RF energy to be applied to the testing samples. Conventionaltesting apparatuses lacked shielding and as a result could only use lowenergy electrical signals. The instrument 100 allows for use of highfrequency RF energy (e.g., 100 kHz-1000 kHz) to be applied to the tissuesamples due to RF shielding provided by the first cylinder 145 a inconjunction with the circular washer 158 and the ring 160. This isparticularly useful for testing tissue reaction to electrosurgicalenergy (e.g., high frequency RF energy) during operating conditions.

Instrument 100 in some instances may utilize portions of ASTM standard D150-98 entitled “Standard test methods for AC loss characteristics andpermittivity (Dielectric Constant) of solid electrical insulation” whenpossible to determine testing methodologies. Since biological tissue isnot a solid electrical insulator, several of the techniques described inthe standards may not be directly applicable to measuring the dielectricproperties of tissue but may be useful in achieving more accurateresults.

Modeling packages, such as those that utilize finite element analysis,may be used to assist in modeling heat transfer and electric fieldsduring RF energy applications. One applicable finite element softwaresystem is known as Etherm. Etherm is used to model heating in biologicalmedia for electrosurgery and other medical applications. The electricalfield component calculates penetration of RF radiation into conductivedielectrics. The information obtained from instrument 100 may beintegrated into Etherm or a similar program to create a more accuratemodel.

A number of different graphical user interfaces (GUI's) could beutilized in this disclosure, one of which includes National Instruments'LabVIEW™. LabVIEW is a software tool for designing test, measurement andcontrol systems. Use of a GUI, such as LabVIEW provides additionalcontrol over the operation of analyzer 280 and allows for moresophisticated simulation.

While several embodiments of the disclosure have been shown in thedrawings, it is not intended that the disclosure be limited thereto, asit is intended that the disclosure be as broad in scope as the art willallow and that the specification be read likewise. Therefore, the abovedescription should not be construed as limiting, but merely asexemplifications of preferred embodiments. Those skilled in the art willenvision other modifications within the scope and spirit of the claimsappended hereto.

1. An instrument for measuring the dielectric properties of material,the instrument comprising: a first electrode assembly and a secondelectrode assembly, the first electrode assembly including a firstelectrode and at least one shaft selectively positionable to move thefirst electrode relative to the second electrode assembly, the secondelectrode assembly including a second electrode; a testing cylindercoupled to the shaft and having an inner cavity defined therein thathouses the first electrode, the testing cylinder being configured toreduce at least one of electric and magnetic currents during activationof the first and second electrodes; and a testing plate which isselectively conformable to receive various types of material therein. 2.An instrument as in claim 1, wherein the testing cylinder is furtherconfigured to reduce at least one of stray radiative RF fields andexternal capacitive leakage currents.
 3. An instrument as in claim 1,wherein, the first electrode assembly and the second electrode assemblyare selectively removable.
 4. An instrument as in claim 1, wherein, thetesting plate is selectively removable.
 5. The instrument according toclaim 1, wherein the testing cylinder includes concentric outer andinner cylinders, the outer cylinder defining the internal cavity and theinner cylinder being formed from an insulative material that reduces atleast one of electric and magnetic currents during activation.
 6. Theinstrument according to claim 5, wherein the testing cylinder includes abottom portion and the outer cylinder and the bottom portion of thetesting cylinder are configured as a Faraday cage.
 7. The instrumentaccording to claim 1, further comprising a plurality of connectioncables, the cables configured to connect an impedance analyzer with thefirst and second electrodes.
 8. The instrument according to claim 7,wherein the impedance analyzer is configured to measure a parameterselected from the group consisting of gain, phase, capacitance,impedance, conductance and loss tangent.
 9. The instrument according toclaim 7, further comprising a graphical user interface (GUI), the GUIconfigured to control the analyzer through a communications port. 10.The instrument according to claim 7, further comprising: a pressuresensor configured to measure pressure exerted by the first electrode onthe material, wherein the impedance analyzer is configured to measure aparameter of the material selected from the group consisting of gain,phase, capacitance, impedance, conductance and loss tangent as pressureis selectively adjusted.
 11. The instrument according to claim 1,wherein the first and second electrodes are constructed of at least oneof stainless steel, titanium, chromium or nickel.